HỘP số tự ĐỘNG AT23

The position of the primary regulator valve is determined by throttle pressure, line pressure and spring tension.. Automatic Transmission Diagnosis - Course 273Primary Regulator Valve Th

Automatic Transmission Diagnosis - Course 273

1 Describe the function of pressure control valves

2 Describe the function of shift control valves

3 Describe the function of timing (sequential) valves

4 Describe the function of pressure modulating valves

5 Explain the effect that throttle pressure and governor pressure have on the shift valves and clutch application

Valve Body Circuits

Lesson Objectives

Automatic Transmission Diagnosis - Course 273

The valve body consists of an upper valve body, a lower valve body, a manual valve body and various covers The body halves are separated

by a separator plate which contains openings that control the flow of fluid between valve circuits The valves control fluid pressure and switch fluid from one passage to another Hydraulic circuits extend to the transmission housing and are connected either by direct mounting

or through oil tube passages

The valves are a precision fit to their bore in the body, and their position in the bore is determined by a balance between spring tension and hydraulic pressure Hydraulic pressure within the valve body will vary based on throttle position or pressure modulating valves In the case of a non−ECT transmission, pressure also varies based on vehicle speed through the governor valve

In order to understand what the many valves do in the valve body, they have been separated by function as listed below:

• Pressure control valves

• Hydraulic control valves

• Timing (Sequencing) valves

• Pressure modulating valves

Valve Body

The body halves are

separated by a separator

plate which contains

openings that control the

flow of fluid between

valve circuits.

Valve Body

Introduction

Pressure control valves regulate hydraulic pressure within the transmission Hydraulic pressure is required to lubricate and remove heat from the fluid Pressure is also necessary to apply the clutches, brakes, and bands that hold planetary gear components of the transmission There are times when high pressure is necessary and other times when it is not The primary concern with high pressure is that engine power is lost and excessive heat is generated Heat breaks down the transmission fluid and robs it of its properties Additional load on the engine affects fuel economy, so by regulating pressure less load is placed on the engine

This valve adjusts the pressure from the oil pump to all the hydraulic circuits in the transmission The purpose of the valve is to reduce engine load and power loss High pressure causes hard shifting and creates more heat reducing fluid life By reducing pressure, less power

is required to rotate the pump and less heat is generated

Pressure has a direct effect on the holding force of clutches and brakes

It should be higher when accelerating the vehicle and lower as the vehicle picks up speed

The output of the valve is called line pressure," the highest oil pressure in the transmission Line pressure is shown in the color red in Toyota publications It is used to apply most clutches and brakes

The position of the primary regulator valve is determined by throttle pressure, line pressure and spring tension Spring tension pushes the valve up for higher line pressure Line pressure is routed to the top of the valve and counters spring tension to reduce line pressure The overall effect is a balance between line pressure and spring tension

At the base of the valve, throttle pressure is applied to push the valve upward, increasing line pressure The greater the throttle opening, the greater line pressure becomes as the pressure regulator valve bleeds off less pressure from the oil pump This is why adjustment of the throttle cable results in a change in shift feel due to the change in line pressure

Pressure

Control Valves

Primary Regulator Valve

Automatic Transmission Diagnosis - Course 273

Primary Regulator Valve

The position of the primary regulator valve

is determined by throttle pressure, line

pressure and spring tension.

Primary Regulator Valve In R-Range

Line pressure from the manual valve is

directed to the bottom of the valve, increasing

line pressure in reverse.

Line pressure is also increased when reverse gear is selected Line pressure from the manual valve is directed to the bottom of the valve pushing it upward, increasing line pressure by as much as 50%

This valve regulates pressure to the torque converter and lubrication pressure Spring tension pushes the valve upward to increase converter pressure Converter pressure acts on the top of the valve to create a balance between it and spring tension In some applications throttle pressure is used to assist the spring in increasing converter pressure Increased secondary regulator pressure provides for a firmer

application of the lockưup clutch under higher torque conditions

Secondary regulator pressure, cooler and lubrication circuits are shown

in yellow in Toyota publications

Secondary

Regulator Valve

Automatic Transmission Diagnosis - Course 273

This valve prevents excessive pressure in the circuit to the oil cooler The circuit is a low pressure system which routes oil through the cooler

in the tank of the radiator and back to the sump of the transmission The valve is spring loaded in the closed position and opens when pressure exceeds the spring rate

Oil Cooler Bypass

The valve is spring

loaded in the closed

position and opens when

pressure exceeds the

spring rate.

This valve regulates the oil pump pressure so that it does not rise above a predetermined maximum value A calibrated spring is used to control the pressure by holding the valve against its seat

Oil Cooler

Bypass Valve

Pressure

Relief Valve

This valve is found on all non−ECT transmissions It is mounted on the output shaft of rear−wheel drive transmissions or is driven from the drive gear on the differential drive pinion/output shaft on front−wheel drive transmissions It balances the line pressure routed from the manual valve and the centrifugal force of the governor weights to produce hydraulic pressure in proportion to vehicle speed The greater the speed of the output shaft, the greater the governor pressure

Below 10 mph, centrifugal force is low and line pressure entering through the drilled passage in the valve to the base of the valve pushes the valve upward blocking the line pressure passage and opening the drain at the top land

Governor Valve

Line pressure to the base

of the valve moves it

upward, opening the

drain port Centrifugal

force does not begin to

push the valve down until

approximately 10 mph.

Governor Valve

Automatic Transmission Diagnosis - Course 273

As vehicle speed increases, the weights move outward and the governor valve is pushed down by the lever of the inner weights The governor valve position is balanced between centrifugal force acting on the lever

at the top of the valve and governor pressure at the base of the valve

As the governor rpm increases (middle and high speed) the outer weight movement is limited by the stopper of the governor body

Increased governor pressure acting on the base of the valve works against spring tension With increased rpms, the centrifugal force of the inner weight and spring tension places additional force to push the valve down

Governor pressure shown in Toyota publications is always green

Governor Valve

Governor pressure

increases as weights

move outward by

centrifugal force.

Throttle pressure is produced in response to throttle opening angle When the accelerator pedal is depressed, the downshift plug pushes the throttle valve upward by means of the spring, creating throttle

pressure The throttle valve supplies throttle pressure to each shift valve and acts in opposition to governor pressure This is why throttle cable adjustment affects shift timing in non−ECT transmissions

Throttle pressure also affects line pressure either directly or through throttle modulator pressure Hydraulic pressure affected by throttle opening is directed to the base of the pressure regulator valve to increase line pressure when engine torque is increased Additional line pressure serves to provide additional holding force at the holding devices to prevent slippage

Throttle pressure shown in Toyota publications is always blue

Throttle Valve

Throttle pressure is

provided to each shift

valve to counter governor

pressure.

Throttle Valve

Automatic Transmission Diagnosis - Course 273

Shift control valves are responsible for directing fluid to different passages in the transmission They can be manually controlled, solenoid controlled, or hydraulically controlled They block hydraulic passages while other lands of the valve open passages

This valve directs line pressure to various passages in the valve body

It is linked to the driver’s selector lever and shifts the transmission into and out of the P, R, N, D, 2 and L−ranges as directed by the driver

As the valve moves to the right, it exposes passages to line pressure which will determine the gear selected The various positions of the valve are maintained by a detent mechanism which also provides feedback to the driver

Manual Valve

Directs line pressure to various

passages in the valve body.

Shift Control Valves

Manual Valve

This valve controls shifting between first and second gears based on governor and throttle pressures The valve is held in position by a calibrated spring located between the low coast shift valve and the 1−2 shift valve When governor pressure is low, but throttle pressure is high, this valve is pushed down by throttle pressure and spring tension As long as there is no governor pressure, there will be no upshift and if throttle pressure is low, upshifts will be early In first gear the forward clutch (C1) is applied through the manual valve, and the No 2 one−way clutch (F2) is holding Line pressure is blocked by the valve from the second brake (B2) and the transmission is held in first gear

As vehicle speed increases, governor pressure overcomes throttle pressure and spring tension at the 1−2 shift valve The circuit to the second brake piston opens, causing the transmission to shift to second gear When the shift valve moves up it covers the throttle pressure passage The downshift occurs when coasting to a stop as spring tension overcomes governor pressure This happens at such a low speed that it is hardly noticeable

A forced downshift from second to first gear occurs when the downshift plug at the base of the throttle valve opens to allow detent regulator pressure to act on the top of the 1−2 shift valve This forces the shift valve down, which opens the second brake piston to a drain and the downshift occurs as the second brake releases

When the selector is placed in the L range, low modulator pressure is applied to the top of the low coast shift valve, holding the 1−2 shift valve in the first gear position

1-2 Shift Valve

Controls line pressure to

the 2nd brake (B2) and

the 2-3 shift valve.

1-2 Shift Valve

Automatic Transmission Diagnosis - Course 273

This valve controls shifting between second and third gears based on throttle and governor pressures The valve is positioned by a calibrated spring located between the intermediate shift valve and the 2−3 shift valve When governor pressure is low, but throttle pressure is high, such as under acceleration, this valve is pushed down by throttle pressure and spring tension, holding the transmission in second gear

When governor pressure rises with increased vehicle speed, this valve is moved upward against throttle pressure and spring tension opening the passage to the direct clutch (C2) piston and causing a shift into third gear

As throttle pressure increases with throttle opening, throttle pressure at the top of the 2−3 shift valve causes the valve to move downward, closing the passage to the direct clutch (C2) The pressure in the direct clutch drains and the transmission is downshifted into second gear

In the event that the accelerator is depressed at or near full throttle, the cam at the base of the throttle valve pushes the detent valve upward This allows detent pressure to assist throttle pressure at the top of the 2−3 shift valve pushing down on the valve, resulting in faster valve movement

In addition, take note that the line pressure which applies the direct clutch (C2) comes through the 1−2 shift valve So if the 1−2 shift valve is stuck there will be no 2nd gear, but also no third gear because the direct clutch cannot be applied

2-3 Shift Valve

Controls line pressure to

the direct clutch (C2).

This line pressure comes

through the 1-2 shift

valve in the second

gear position.

2-3 Shift Valve

When the gear selector is placed in the 2−range, line pressure from the manual valve acts on the intermediate shift valve The 2−3 shift valve descends causing a downshift into second gear and preventing an upshift to third gear Also, line pressure passes through the second modulator valve and 1−2 shift valve and acts on the second coast brake (B1) to effect engine braking

This valve controls shifting between third and forth gears based on governor and throttle pressures The valve is held in position by a calibrated spring located at the top of the 3−4 shift valve which transfers the tension and holds the 3−4 shift valve down Line pressure controlled by the 3−4 shift valve comes from the oil pump directly Whenever the pump is turning, pressure is directed through the 3−4 shift valve to either the overdrive direct clutch (C0) or the overdrive brake (B0) When the overdrive direct clutch is applied, the overdrive unit is in direct drive When the overdrive brake is applied, the overdrive unit is in overdrive

When governor pressure is low, but throttle pressure is high, this valve

is pushed down by throttle pressure and spring tension When vehicle speed increases, governor pressure rises At some point it overcomes throttle pressure and moves the valve upward, diverting line pressure from the overdrive direct clutch (C0) to the overdrive brake (B0) and resulting in an upshift to overdrive

3-4 Shift Valve

Controls line pressure to

the overdrive brake (B0)

and overdrive direct

clutch (C0).

3-4 Shift Valve

Automatic Transmission Diagnosis - Course 273

The downshift plug is located below the throttle valve It is actuated by the throttle cam in response to engine throttle movement when the driver presses down on the accelerator, opening it more than 85% It is used in a governor−controlled transmission to enhance downshifting rather than relying on throttle pressure alone to overcome governor pressure and move the shift valve down The net result is that a downshift occurs at a higher vehicle speed than if relying on throttle pressure alone

When the throttle is opened 85% or more, the downshift valve moves upward and detent regulator pressure is directed to each shift valve to counter governor pressure Detent pressure provides added force in addition to throttle pressure and spring tension to move the valve downward against governor pressure Depending on the vehicle speed, governor pressure may be great enough to allow the 1−2 shift valve and 2−3 shift valve to remain up, whereas the 3−4 shift valve may

immediately move downward to cause a 4 to 3 downshift

Downshift Plug

Enhances downshifting

rather than relying on

throttle pressure alone to

overcome governor

pressure in a forced

downshift.

Downshift Plug